1. Field of the Invention
The present invention relates to a process for preparing a polyarylene sulfide and to a novel polyarylene sulfide prepared thereby.
More particularly, the present invention relates to a process for preparing a polyarylene sulfide, in which a hydrous alkali metal sulfide commercially available is used without dehydration and a polymerization promoter can be recovered with ease. The polyarylene sulfide produced is high in its degree of whiteness, the molecular weight of the polyarylene sulfide so produced is sufficiently high, and it is suitable for molding materials for various molded articles, films, fibers, and mechanical, electric and electronic parts.
The present invention can prevent color from being imparted, by the presence of by-products and the like, to the polyarylene sulfide containing a carbonyl group while permitting the high recovery rate of an organic polar solvent, the polyarylene sulfide of this invention being different in solubility from usual polyarylene sulfides. The process can allow the efficient production of the polyarylene sulfide with a high degree of whiteness in high yields.
Furthermore, the novel polyarylene sulfide according to the present invention can be prepared under specified production condition, it is high in its degree of whiteness, it has a resistance to heat as high as the usual polyarylene sulfides, and it is different in solubility from the usual polyarylene sulfides.
2.Description of Related Art
The polyarylene sulfides such as polyphenylene sulfide are thermoplastic while being partially thermosetting, and they have superior properties as engineering plastics, such as excellent resistance to chemicals, favorable mechanical strength over a broad temperature range, and good thermal rigidity.
The polyarylene sulfides such as polyphenylene sulfide have been heretofore prepared by various processes.
U.S. Pat. No. 3,354,129 proposes a process for preparing polyarylene sulfides in which a polyhalogen aromatic compound, such as a dihalogen aromatic compound, is reacted with an alkali metal sulfide in an organic polar solvent.
U.S. Pat. No. 3,919,177 and Japanese Patent Publication (Kokoku) No. 12,240/1977 propose processes for preparing polyarylene sulfides having a high intrinsic viscosity and low melt flowability, in which a p-dihalobenzene is polymerized with an alkali metal sulfide or an alkali metal bisulfide (an alkali metal hydrosulfide, or an alkali metal hydrogen sulfide) as a sulfur source or another appropriate sulfur compound (for example, thiourea, thioamide, thiocarbamate, thiocarbonate, mercaptan, mercaptide, mercaptocarboxylic acid, or the like) to be used with at least one member of a base, in the presence of a promoter such as a carboxylate (a carboxylic acid of the carbohydryl system having from 1 to 20 carbon atoms), e.g., sodium acetate or lithium acetate, in an organic amide.
U.S. Pat. No. 4,116,947 discloses a process for preparing branched polyarylene sulfides having a relatively high molecular weight by contacting a p-dihalobenzene and a polyhalogen aromatic compound with an alkali metal sulfide in the absence or presence of a sodium carboxylate in an N-alkyllactam in an amount of water of 1.2 to 2.4 moles with respect to mole of the alkali metal sulfide.
Those processes, however, present the disadvantages that the water content in the polymerization system needs to be set at a relatively low value within a narrow range in order to provide the polymer with a high production efficiency, which has such a high molecular weight as being highly valuable.
In usual cases, commercially available alkali metal sulfides and hydrosulfides contain a considerably large amount of water so that, if such compounds are employed as a raw material for polymerization as they are, the resulting polymers are not provided with a sufficiently high molecular weight, and a color is imparted to the resulting polymers.
For these reasons, the conventional processes require the alkali metal sulfides or hydrosulfides available usually as a hydrate to be dehydrated prior to polymerization, thereby removing water from the hydrous sulfides or hydrosulfides to reduce a large water content to a relatively low value within a narrow range. Accordingly, the conventional processes require at least two steps, such as dehydration and polycondensation steps. The provision of a dehydration step presents the following disadvantages. The dehydration step is usually carried out by means of a distillation in the presence of a polar solvent. However, a stainless steel reactor may get eroded and impurities may be dissolved from the inner wall of the reactor into the polar solvent, thereby impairing the purity and whiteness of the resulting polyarylene sulfide, or transforming the polar solvent to be recovered.
Furthermore, Japanese Patent Publication (Kokai) No. 22,926/1984 discloses a process in which a dihalogen aromatic compound is reacted with a substantially anhydrous metal sulfide and a metal carbonate in the presence of a minute amount of water. This process, however, produces a large amount of by-products, such as oligomers, and provides polyarylene sulfides with an insufficiently high molecular weight. The yield of the resulting polymer is low. Furthermore, a long period of time is required for enlargement of the molecular weight of the resulting polymer, so that this process is industrially disadvantageous.
The processes disclosed in U.S. Pat. Nos. 3,919,177 and 4,116,947 and Japanese Patent Publication No. 12,240/-1977 further suffer the disadvantages that a recovery and re-use of the polymerization promoter, such as sodium acetate or lithium acetate, is difficult. In order to recover the polymerization promoter, the process becomes so complicated that the economy is worsened. If the polymerization promoter is discharged into a water sewage system, a pollution problem arises.
Furthermore, the process disclosed in U.S. Pat. No. 4,116,947 uses a polyhgalogen aromatic compound as a branching agent, thereby enlarging molecular weights of branched polyphenylene sulfides.
As other processes for enlarging a molecular weight of a polyarylene sulfide, Japanese Patent Publication (Kokoku) No. 7,332/1986 propose processes, however, they present the disadvantage that the resulting polymers are likely to get gelled so that they pose problems with manufacture and quality.
Furthermore, the process disclosed in U.S. Pat. No. 4,116,947 has the drawback that the organic polar solvent used is restricted to expensive solvents, such as the lactams.
For instance, U.S. Pat. No. 3,867,356 discloses a process in which a dihalogen aromatic compound is reacted with an alkali metal hydrosulfide in an organic amide compound as a solvent in the presence of an alkali metal aminocarboxylate as represented by the general formula: EQU R.sub.2 N(CR.sub.2).sub.n CO.sub.2 M
where
R is a hydrogen atom, an alkyl group, a cycloalkyl group or an aryl group, or a combination thereof; PA1 M is lithium, sodium, potassium, rubidium or cesium; and PA1 n is an integer from 1 to 12.
This process, however, presents the problem that the resulting polyarylene sulfide is colored due to by-products created by the side reactions between the polyhalogen aromatic compound and the alkali metal aminocarboxylate, thereby not yielding polyarylene sulfides with a high degree of whiteness and with a high molecular weight.
U.S. Pat. No. 3,869,433 proposes a process in which an alkali metal hydroxide is present in the reaction of a polyhalogen aromatic compound with an alkali metal hydrosulfide in an organic amide compound as a solvent. In this process, however, the organic amide compound is decomposed so that the solvent cannot be recovered and reused. This is industrially disadvantageous. Furthermore, the resulting polyarylene sulfide is colored, whereby polyarylene sulfide with a high degree of whiteness is not made.
U.S. Pat. No. 3,876,591 discloses a process for preparing polyarylene sulfides, in which an alkali metal hydrosulfide is used at amounts by 0.8 to 1.5 times of the molar amount of a polyhalogen aromatic compound. This process produces a large quantity of oligomers as by-products, thereby lessening the yield of the polyarylene sulfide and not providing polyarylene sulfide with a high molecular weight.
These conventional processes have the drawbacks that polyarylene sulfides cannot be prepared which have sufficient melt properties and unique characteristics such as functional groups. Thus demands have been made to provide novel polyarylene sulfides and a process for the preparation thereof in order to satisfy demands for various and diversified properties.